Sumanenylferrocenes and their solid state self-assembly

The first ferrocene-fused organometallic compounds derived from the buckybowl sumanene (C21H12) are presented. Both compounds, sumanenylferrocene and 1,1′-disumanenylferrocene, have been synthesized by Negishi-type cross- coupling of iodosumanene and were studied crystallographically. Sumanenylferrocenes form unique packing motifs, which are both different from those of their corannulene congeners and sumanene itself

Pre-steady-state kinetic studies of redox reactions catalysed by Bacillus subtilis ferredoxin-NADP+ oxidoreductase with NADP+/NADPH and ferredoxin

Ferredoxin-NADP+ oxidoreductase ([EC1.18.1.2], FNR) from Bacillus subtilis (BsFNR) is a homodimeric flavoprotein sharing structural homology with bacterial NADPH-thioredoxin reductase. Pre-steady-state kinetics of the reactions of BsFNR with NADP+, NADPH, NADPD (deuterated form) and B. subtilis ferredoxin (BsFd) using stopped-flow spectrophotometry were studied. Mixing BsFNR with NADP+ and NADPH yielded two types of charge-transfer (CT) complexes, oxidized FNR (FNRox)-NADPH and reduced FNR (FNRred)-NADP+, both having CT absorption bands centered at approximately 600 nm. After mixing BsFNRox with about a 10-fold molar excess of NADPH (forward reaction), BsFNR was almost completely reduced at equilibrium. When BsFNRred was mixed with NADP+, the amount of BsFNRox increased with increasing NADP+ concentration, but BsFNRred remained as the major species at equilibrium even with about 50-fold molar excess NADP+. In both directions, the hydride-transfer was the rate-determining step, where the forward direction rate constant (~ 500 s- 1) was much higher than the reverse one (< 10 s- 1). Mixing BsFdred with BsFNRox induced rapid formation of a neutral semiquinone form. This process was almost completed within 1 ms. Subsequently the neutral semiquinone form was reduced to the hydroquinone form with an apparent rate constant of 50 to 70 s- 1 at 10 °C, which increased as BsFdred increased from 40 to 120 μM. The reduction rate of BsFNRox by BsFdred was markedly decreased by premixing BsFNRox with BsFdox, indicating that the dissociation of BsFdox from BsFNRsq is rate-limiting in the reaction. The characteristics of the BsFNR reactions with NADP+/NADPH were compared with those of other types of FNRs. © 2016 Elsevier B.V. All rights reserved.Embargo Period 12 month

Purification and characterization of ferredoxin–NAD(P)+ reductase from the green sulfur bacterium Chlorobium tepidum

Ferredoxin–NAD(P)+ reductase [EC 1.18.1.3, 1.18.1.2] was isolated from the green sulfur bacterium Chlorobium tepidum and purified to homogeneity. The molecular mass of the subunit is 42 kDa, as deduced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular mass of the native enzyme is approximately 90 kDa, estimated by gel-permeation chromatography, and is thus a homodimer. The enzyme contains one FAD per subunit and has absorption maxima at about 272, 385, and 466 nm. In the presence of ferredoxin (Fd) and reaction center (RC) complex from C. tepidum, it efficiently catalyzes photoreduction of both NADP+ and NAD+. When concentrations of NADP+ exceeded 10 μM, NADP+ photoreduction rates decreased with increased concentration. The inhibition by high concentrations of substrate was not observed with NAD+. It also reduces 2,6-dichlorophenol-indophenol (DPIP) and molecular oxygen with either NADPH or NADH as efficient electron donors. It showed NADPH diaphorase activity about two times higher than NADH diaphorase activity in DPIP reduction assays at NAD(P)H concentrations less than 0.1 mM. At 0.5 mM NAD(P)H, the two activities were about the same, and at 1 mM, the former activity was slightly lower than the latter

Tris[2-(deuteriomethyl­sulfan­yl)­phen­yl]­phosphine deuteriochloro­form 0.125-solvate

The title deuterated tripodal phosphine, C21H12D9PS3·0.125CDCl3, crystallizes as two independent mol­ecules, one of which lies on a general position and the other about a threefold rotation axis, and as a deuteriochloro­form solvate. The solvent mol­ecule is disordered about a site of symmetry 3, so that the ratio of phosphine to solvent is 8:1. The P atom adopts a pyramidal coordination geometry

Room-Temperature Reversible Chemisorption of Carbon Monoxide on Nickel(0) Complexes

Chemisorption on organometallic-based adsorbents is crucial for the controlled separation and long-term storage of gaseous molecules. The formation of covalent bonds between the metal centers in the adsorbents and the targeted gases affects the desorption efficiency, especially when the oxidation state of the metal is low. Herein, we report a pressure-responsive nickel(0)-based system that is able to reversibly chemisorb carbon monoxide (CO) at room temperature. The use of N-heterocyclic carbene ligands with hemi-labile N-phosphine oxide substituents facilitates both the adsorption and desorption of CO on nickel(0) via ligand substitution. Ionic liquids were used as the reaction medium to enhance the desorption rate and establish a reusable system. These results showcase a way for the sustainable chemisorption of CO using a zero-valent transition-metal complex.Yamauchi Y., Hoshimoto Y., Kawakita T., et al. Room-Temperature Reversible Chemisorption of Carbon Monoxide on Nickel(0) Complexes. Journal of the American Chemical Society , (2022); https://doi.org/10.1021/jacs.2c02870

Reversible Modulation of the Electronic and Spatial Environment around Ni(0) Centers Bearing Multifunctional Carbene Ligands with Triarylaluminum

Designing and modulating the electronic and spatial environments surrounding metal centers is a crucial issue in a wide range of chemistry fields that use organometallic compounds. Herein, we demonstrate a Lewis-acid-mediated reversible expansion, contraction, and transformation of the spatial environment surrounding nickel(0) centers that bear N-phosphine oxide-substituted N-heterocyclic carbenes (henceforth referred to as (S)PoxIms). Reaction between tetrahedral (syn-κ-C,O-(S)PoxIm)Ni(CO)2 and Al(C6F5)3 smoothly afforded heterobimetallic Ni/Al species such as trigonal-planar {κ-C-Ni(CO)2}(μ-anti-(S)PoxIm){κ-O-Al(C6F5)3} via a complexation-induced rotation of the N-phosphine oxide moieties, while the addition of 4-dimethylaminopyridine resulted in the quantitative regeneration of the former Ni complexes. The corresponding interconversion also occurred between (SPoxIm)Ni(η2:η2-diphenyldivinylsilane) and {κ-C-Ni(η2:η2-diene)}(μ-anti-SPoxIm){κ-O-Al(C6F5)3} via the coordination and dissociation of Al(C6F5)3. The shape and size of the space around the Ni(0) center was drastically changed through this Lewis-acid-mediated interconversion. Moreover, the multinuclear NMR, IR, and XAS analyses of the aforementioned carbonyl complexes clarified the details of the changes in the electronic states on the Ni centers; i.e., the electron delocalization was effectively enhanced among the Ni atom and CO ligands in the heterobimetallic Ni/Al species. The results presented in this work thus provide a strategy for reversibly modulating both the electronic and spatial environment of organometallic complexes, in addition to the well-accepted Lewis-base-mediated ligand-substitution methods.Yamauchi Y., Mondori Y., Uetake Y., et al. Reversible Modulation of the Electronic and Spatial Environment around Ni(0) Centers Bearing Multifunctional Carbene Ligands with Triarylaluminum. Journal of the American Chemical Society 145, 16938 (2023); https://doi.org/10.1021/jacs.3c06267

Purification and characterization of ferredoxin-NADP(+) reductase encoded by Bacillus subtilis yumC

From Bacillus subtilis cell extracts, ferredoxin-NADP+ reductase (FNR) was purified to homogeneity and found to be the yumC gene product by N-terminal amino acid sequencing. YumC is a ～ 94-kDa homodimeric protein with one molecule of non-covalently bound FAD per subunit. In a diaphorase assay with 2,6-dichlorophenol-indophenol as electron acceptor, the affinity for NADPH was much higher than that for NADH, with Km values of 0.57 μM vs >200 μM. Kcat values of YumC with NADPH were 22.7 s–1 and 35.4 s–1 in diaphorase and in a ferredoxin-dependent NADPH-cytochrome c reduction assay, respectively. The cell extracts contained another diaphorase-active enzyme, the yfkO gene product, but its affinity for ferredoxin was very low. The deduced YumC amino acid sequence has high identity to that of the recently identified Chlorobium tepidum FNR. A genomic database search indicated that there are more than 20 genes encoding proteins that share a high level of amino acid sequence identity with YumC and which have been annotated variously as NADH oxidase, thioredoxin reductase, thioredoxin reductase-like protein, etc. These genes are found notably in gram-positive bacteria, except Clostridia, and less frequently in archaea and proteobacteria. We propose that YumC and C. tepidum FNR constitute a new group of FNR that should be added to the already established plant-type, bacteria-type, and mitochondria-type FNR groups

Purification of ferredoxins and their reaction with purified reaction center complex from the green sulfur bacterium Chlorobium tepidum

Four ferredoxin (Fd) fractions, namely, FdA–D were purified from the green sulfur bacterium Chlorobium tepidum. Their absorption spectra are typical of 2[4Fe–4S] cluster type Fds with peaks at about 385 and 280 nm and a shoulder at about 305 nm. The A385/A280 ratios of the purified Fds were 0.76–0.80. Analysis of the N-terminal amino acid sequences of these Fds (15–25 residues) revealed that those of FdA and FdB completely agree with those deduced from the genes, fdx3 and fdx2, respectively, found in this bacterium (Chung and Bryant, personal communication). The N-terminal amino acid sequences of FdC and FdD (15 residues) were identical, and agree with that deduced from the gene fdx1 (Chung and Bryant, personal communication). The A385 values of these Fds were unchanged when they were stored for a month at −80°C under aerobic conditions and decreased by 10–15% when they were stored for 6 days at 4°C under aerobic conditions, indicating that they are not extremely unstable. In the presence of Fd-NADP+ reductase from spinach, and a purified reaction center (RC) preparation from C. tepidum composed of five kinds of polypeptides, these Fds supported the photoreduction of NADP+ at room temperature with the following Km and Vmax (in μmol NADP+ μmol BChl a−1 h−1): FdA, 2.0 μM and 258; FdB, 0.49 μM and 304; FdC, 1.13 μM and 226; FdD, 0.5 μM and 242; spinach Fd, 0.54 μM and 183. The Vmax value of FdB was more than twice that previously reported for purified RC preparations from green sulfur bacteria